I would go with invisibility. Time travel can mess stuff up.
EDIT: I'm glad this is back. Many memories in this thread.
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Time Travel would be interesting, but if you're traveling in time relative to your location in the Universe, you may very well time travel back a few months and realize that earth is not in the same position it was before, which puts you in the middle of space, which makes you 230.78% -blam!-ed. Invisibility would be much less likely to, you know, dump you literally, in the middle of no-where.